(a) Field of the Invention
The present invention relates to an engine of a vehicle and more particularly, a rocker arm for a variable valve lift (VVL) apparatus and a variable valve lift apparatus having the same.
(b) Description of the Related Art
An internal combustion engine generates power by burning fuel in a combustion chamber in an air media that is drawn into the chamber. Intake valves are operated by a camshaft in order to take in the air, and the air is drawn into the combustion chamber while the intake valves are open. In addition, exhaust valves are operated by the camshaft, and a combustion gas is exhausted from the combustion chamber while the exhaust valves are open.
An optimal operation of the intake valves and the exhaust valves depends on a rotation speed of the engine. That is, optimal opening/closing timing of the valves or an optimal lift depends on the rotation speed of the engine. In order to achieve such an optimal valve operation depending on the rotation speed of the engine, research has been undertaken on a variable valve lift (VVL) apparatus that enables different valve lifts depending on the engine speed.
As an example of the VVL apparatus, a hydraulic line is formed for each desired valve lift, and oil supply to the hydraulic line is controlled by an oil control valve (OCV).
According to such a scheme, in order to achieve a variety of valve lifts, the number of hydraulic lines should be increased or a greater number of OCVs should be employed even though the OCV typically occupies a large volume in the cylinder head. Considering that the cylinder head has limited space, only a limited number of OCVs can be installed in the cylinder head, and an increase of the number of the OCVs employed results in complexity of a hydraulic circuit in the cylinder head and an increase of manufacturing cost.
Therefore, if a VVL apparatus may be realized by merely redesigning a single part (e.g., a rocker arm), an improvement of performance of an engine may be expected without incurring substantial cost, and a smaller-size and higher-performance engine may be achieved.
In addition, research has been undertaken on a cylinder deactivation function in which a specific cylinder may be deactivated when the engine may be operated at a relatively low output power. This cylinder deactivation enables improvement of fuel consumption of the engine without deteriorating maximum power of the engine.
Accordingly, if an improved VVL apparatus enables such a cylinder deactivation function, performance of the engine may be improved in various aspects with minimal cost and space loss of the engine.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.